Hey guys, first post on this site.
A couple times now I’ve had a strange problem happen in my 2008 Ford Taurus X. Driving at cruising speeds (50+), the car’s engine light, airbag light, TPM sensor will all come on and stay on for a few minutes. Also, the speedometer will zero out and the transmission will seem to shift to a higher gear. When this happened yesterday, I had to move a few lanes over (rush hour, I-95) to try and get to the side of the road. By the time I worked over two lanes, the problem was gone. The same thing happened today, and I figured it’d go away in a couple minutes, so I kept driving. It didn’t go away, so I pulled over and turned the engine off. When I restarted the engine, the problem went away, but the car was still in the higher gear, so it lugged along the side for a second until it reached 20 mph to merge and then shifted roughly and is apparently now driving fine. My first thought is that I have a bad speed sensor, any ideas what the problem could be?
Sounds like the CAN network is either going down or has one or more nodes that are not responding. Vehicle has 2 networks that are used for communicating operating parameters between all of the vehicles control modules. The instrumentation tell tales are illuminating because the instrument cluster module has identified critical information is missing. Sometimes the networks will reset/reboot themselves. If the concern happens for a longer period of time, the network/s will not restart until the key is cycled.
CAN networks can crash for a variety of reasons: (Can be intermittent or a hard fault)
- CAN Bus +/- circuits shorted to power or ground.
- Bus circuits shorted together.
- Connector terminal pit fit issues for bus wiring. (Simply means that the connector terminals are loose between the male and female connector terminals/pins.)
- Failing module on the network.
- Bus circuit continuity/resistance. (HS CAN should measure 60 ohms resistance between HS CAN +/-. If 120 ohms is present, one of the termination resistors has been removed/disconnected)
Someone needs to record all the U-codes from the vehicle and record where (Module) the U-codes were stored. Sometimes the codes can offer the smoking gun as to who went down. The codes may offer some insight as to where the harness issue may reside. Who ever pulls the codes MUST be specific on code to module locations… Example… PCM had U0401 ABS had U0150 etc… if done correctly, sometimes you can see a pattern in the codes and find the faulty component easily.
Curious if you have had any recent work done to the vehicle? Any radio, dash, HVAC, interior work done recently? Sometime issues like this can be triggered by connectors that are not fully latched/seated. Also we (Technicians) are seeing increases on Network faults due to add-on accessories like vehicle data recorders used by insurance companies… (Devices that plug into the Diagnostic Data Port under the driver’s side of the dash panel.)
I’ve seen this problem on a Taurus before. I wasn’t involved in the diagnosis, but it’s possible that there’s an existing Technical Service Bulletin on this. You may want to call the dealer’s parts department and ask.
Jgree sounds like he’s been in-depth involved in this system, and perhaps has a tap into Ford’s databanks. Perhaps he has access to any relevant TSBs???
Interesting, I’ll go to our local mechanic and ask them to pull the codes. The only thing we’ve done in this car (beyond maintenance) is to replace the battery when it went bad about 5k miles ago. I’ll let you guys know what comes of the visit to the mechanic. Thanks!
No TSBs relevant to this concern… Let us know what they find
Taking a chance this has any interest still. My 2008 Ford Taurus X has just created the same symptoms, and I am looking for advice.
Driving at 65mph on the highway, 3/4 tank of gas, with cruise control on, nice dry 85° day… the low fuel warning beeps in the dash, the tranny seems to downshift or overdrive kicks “off” immediately, I look down at the cluster to see the speedometer goes to zero mph, the RPM is around 3200, and the fuel gauge is empty, low fuel light on, and the service engine “wrench light” was illuminated. I touched the gas pedal, and it accelerated and within a few seconds the speedo went back to 65 mph, the warning lights went off and all went back to normal like nothing happened. All seems fine today. Any ideas?
Same situation… CAN bus (the vehicle computer network or internet between computers) has been compromised. All of the modules share data with each other… If one module stops transmitting or the message gets “jammed” due to a circuit/wire issue, the other module/s who rely on that data basically get pissed off and go into a failsafe mode.
Failsafe modes for the instrument cluster is always, gauges going to zero and MIL lamps coming on. Failure modes for the engine management system often include dropping to a default transmission gear.
If the module comes back online, or the wiring short circuit or poor connection is resolved, (due to vibration, moisture reduction or other) the CAN bus will reset automatically (in most cases) and the indicators will go out. Module diagnostic trouble codes typically result from CAN bus problems.
If you’re trying to figure out what is happening and why, you really need a scan tool. The Ford tool can display all of the DTCs (trouble codes) and which module is reporting them… Based on the codes and module location, combined with a vehicle wiring schematic, the location can usually be identified.
Most of the time CAN bus problems are a result of wiring issues. (Wire chaffs, short circuits, loose connectors, loose terminal pin fit, etc.) Pin fit issues are very common if you had any resent electrical work done to the vehicle where the technician was using the wrong test probes.
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